How do you calculate running heart rate zones?
Anchor them to heart rate reserve and to your lactate thresholds rather than to a percentage of maximum, and treat the boundaries as soft.
The most defensible zone scheme for distance running has three bands rather than five, anchored to physiology rather than to round numbers: Zone 1 below LT1, Zone 2 between LT1 and LT2, Zone 3 above LT2. In heart-rate-reserve terms that puts the LT1 boundary around 65–75% and the LT2 boundary around 80–88%.
Five- and seven-zone schemes subdivide those bands further. They are not wrong, but the extra boundaries are conventions rather than physiological landmarks, and treating a zone edge as meaningful when it is really a rounding decision leads to a lot of unproductive precision.
To build your own: measure resting heart rate over several mornings, establish maximum from a genuinely maximal effort rather than a formula, then compute reserve and apply the percentages. Cross-check against a recent race — if your calculated LT2 heart rate is far from what you actually sustained in a 10 km, trust the race.
Remember what shifts them. Heat, dehydration, altitude, illness, caffeine and accumulated fatigue all move heart rate at a given pace, sometimes by 5–10 beats. Zones are a guide to effort, not a contract, and on a hot day the same zone means a slower pace.
Key numbers
| Zone 1 | <65–75% HRR | below LT1 |
|---|---|---|
| Zone 2 | ~75–85% HRR | between thresholds |
| Zone 3 | >80–88% HRR | above LT2 |
Work it out for yourself
HR pacing simulator — Generate your zones and see how heat and hydration shift them.
Frequently asked questions
How many heart rate zones should I use?
Three is enough for most distance runners and maps directly onto the physiology: easy, threshold-ish, hard. Five-zone schemes add resolution that is mostly convention, though they are fine if your training platform already uses them.
Why is my heart rate higher on hot days at the same pace?
Because blood is diverted to the skin for cooling and plasma volume falls with sweating, so the heart compensates with rate. Treat the zone as the target and let pace fall — running the same pace in heat means running a higher intensity than you intended.
Sources
- Seiler (2010). What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance.
- Swain & Leutholtz (1997). Heart rate reserve is equivalent to %VO₂ reserve. Medicine & Science in Sports & Exercise.
Related explainers
Glossary: HRR (Heart Rate Reserve), LT1 (Lactate Threshold 1), LT2 (Lactate Threshold 2)